This invention relates generally to touch sensitive systems, and more particularly to touch panels that detect bending waves.
Touch sensitive systems are used to provide two-dimensional coordinate information. One example may be an opaque track pad while another example may be a transparent touchscreen placed in front of a display such as a liquid crystal display. Touch sensitive systems may be based on a variety of touch technologies including resistive, such as three-wire, four-wire, five-wire and nine-wire, capacitive, infrared and surface acoustic wave types, as well as bending-wave touch technologies.
In one approach, bending-wave touch systems may detect a touch based on a tap of an object, such as a key or finger, which excites bending waves in a substrate. These bending waves induce electrical signals in piezoelectric elements or sensors (piezos) bonded to the substrate. These signals are captured by electronics and processed to determine a set of (X,Y) coordinates of the touch position, such as by using matching algorithms that utilize acoustic fingerprints or by using time-of-flight methods to extract touch coordinate information from piezo signals.
Touch sensitive systems are used in many different applications, such as small hand-held devices such as phones, cameras and personal digital assistants, restaurants, banks and automated teller machines, museums and the like. Touch panel construction that is compact and durable, and which reliably detects touch events, is desirable for use in bending-wave touch systems. Furthermore, it is desirable that the system including both the touch screen and display is of a compact mechanical design.